Improvement is sought for an approach to the delivery of macromolecular agents to solid tumors and other diseased tissue. The approach, which has been termed "convection-enhanced delivery", is one of delivery to target tissue interstitium by infusion. Infused agents are carried through the interstitium by the bulk flow of the infusate solution to achieve more rapid spatial spread than would occur by diffusion. Typically, such infusions have been limited to submicroliter per minute flow rates by the occurrence of undesired leakage along the track of the infusion cannula. This limitation may be overcome by cannula modification to provide a greater surface area for entry of the infusate into the tissue. Various cannula designs are being investigated.